In general, an ozonizer by electrolysis includes a pair of opposing electrodes and a solid polymer electrolyte therebetween. A desired electric current is applied to the electrodes in water, and a high-concentration of ozone dissolved in water can be produced by electrolysis of water.
Conventionally, ozone water may be produced by two types of methods.
According to one of the conventional methods, ozone is evolved by means of corona-type electrical discharges, and the evolved ozone is fed to and dissolved into water to produce ozone water. This method necessitates a blower for feeding air and a micro-bubbler for facilitating dissolution of ozone into water. However, it leads to increase in the manufacturing cost and decrease in the production efficiency, along with noise associated therewith. In addition, undesired nitrogen oxides are produced during the corona electrical discharge by oxidation of nitrogen in air.
In the other type of method, ozone of molecular state can be produced directly in water, and thus it may solve the problems in the above-described technique. This method is categorized into a membrane type and non-membrane type, depending on the presence of solid polymer electrolyte in the construction of opposing electrodes in water.
In the membrane-type process, which is exemplified by U.S. Pat. No. 4,836,929, a lead electrode and a platinum black electrode serve as an anode and a cathode respectively, and a membrane made of solid polymer electrolyte is inserted therebetween. It is, however, technically very difficult to uniformly install the electrodes and the solid polymer electrolyte. Furthermore, due to non-uniformity such as a localized overpressure during operation, the solid polymer electrolyte can be locally deteriorated during electrolysis, and it results in significant reduction in the life span.
U.S. Pat. No. 4,416,747 discloses an electrode assembly in which the surface of solid polymer electrolyte is coated with a precious metal, such as platinum. However, this electrode assembly cannot be easily manufactured in practice, and the production cost thereof is very high. Moreover, it is technically unstable, which leads to lack of reliability.
On the other hand, during the generation of ozone by electrolysis, the formation of a scale is inevitably associated. In order to avoid the scale formation, the conventional technique in the prior art has used a purified water in which 2+ cation constituents such as calcium and magnesium, which causes the scale, has been removed. There is, therefore, a limitation in the applications thereof.
That is, when the electrolysis takes place without removing 2+ cation such as calcium and magnesium from the feed water, for example, by using a hard acidic cation-exchange resin or a reverse osmosis process, OH− ion generated in the equation (5) is used to precipitate hydroxides as in the equations (6) and (7) so that a scale is formed on the surface of the cathode and thus the efficiency of electrolysis is reduced.2H2O+2e→H2+2OH−  (5)Ca2++2OH→Ca(OH)2(↓)  (6)Mg2++2OH→Mg(OH)2(↓)  (7)
In the case of non-membrane type, which is exemplified by Korean Patent No. 36389 entitled “a method and apparatus for producing ozone in water,” a multiple pair of opposing electrodes formed of platinum-group metals are placed in water, and electric current is applied to the opposing electrodes such that a strong electric field can be concentrated therearound. Therefore, ozone can be directly evolved in water.
In the above-described prior art, however, when tap water or similar grade water is employed as the feed water, due to lack of electrolyte for current flow in water, a higher electric voltage is required for the electrolysis of water, thereby increasing the electric power consumption and thus reducing the life of electrodes.
Alternatively, in the case where distilled water or purified water by a cation-exchange resin is supplied, the current-flow though the water via the electrodes is significantly suppressed. Therefore, there is a limitation in practical applications.
As another solution to the prior art problems, Korean patent application No. 10-200-0011202 entitled “An Apparatus for Producing High-Concentration Ozone in Water” proposes a technique, in which a vibrator is mounted inside the electrolytic bath of the ozonizer in order to remove the micro-bubbles forming and growing on the surface of the electrodes. The mere suppression of bubbles does not become an ultimate solution to the general problems in the prior art.